1. Field of the Invention
The present invention relates to parachute systems generally for controlling the opening characteristics of parachutes, especially conventional round parachutes. More particularly, this invention relates to reefing systems or devices for slowing the opening or inflation of round or other generally axisymmetrical parachutes to reduce shock and to control the shape of the lower edge of the canopy during opening, especially in larger parachutes.
2. Description of the Prior Art
Parachutes have long been used to lower personnel and unmanned cargo to the ground from airplanes and other airborne craft. A known problem with the use of parachutes is the sudden shock when the canopy of the parachute opens and fills quickly with air. This is especially serious at high speeds where the canopy fills more rapidly. Also, in more recent years, some parachutes have been made with low permeability or zero permeability fabrics, and the opening shock with such parachutes is more severe than with parachutes made with highly permeable fabrics.
Further, as payloads being delivered by parachute have become larger and heavier, the usage of larger parachutes has become necessary. However, such larger parachutes can display undesirable inflation characteristics which limit the practical size of such parachutes. Moreover, it is difficult to control the shape of the lower edge of the large canopy to maintain a symmetric circular shape of the parachute during initial stages of inflation. Such parachutes tend to form in-folded portions and thus do not operate according to the designed inflation characteristics, thus often resulting in structural failure.
Therefore, in the design and use of parachutes for the aerial delivery of a payload, whether for personnel, cargo, or the like, there are several factors to consider. Among these are: (a) the overall flight envelope, including airspeed and altitude, of the aircraft whether fixed wing, helicopter, missile, etc. used to transport and drop the payload to be delivered by the parachute; (b) the overall parachute recovery envelope required for the payload; (c) the minimum acceptable opening altitude; (d) the maximum allowable opening force which can be sustained by the payload or person; (e) other factors such as the allowable weight and pack volume of the parachute. Further, the parachute must be designed to operate with opening forces that do not damage the parachute itself.
One early reefing system to control opening shock was a generally round device, called a "slider" which had rings or grommets around its periphery. All of the suspension lines of the parachute extended through these rings. The panel may or may not have had a center opening and may or may not have been made of a permeable cloth. See, for example, U.S. Pat. No. 4,863,119.
Another device directed to the problem of opening shock is called a reefing line. In this device, a reefing line or cord passes through small rings attached to the skirt of the canopy, and the length of the line or cord determines the reefed diameter of the parachute during inflation. A line cutter then severs the reefing line after a predetermined time delay, allowing the parachute to continue inflation, until the canopy is completely inflated. This system has the disadvantage of being a fixed time delay.
Another device for controlling opening shock is the use of a small canopy mounted inside the main parachute canopy. A series of lines extend from the small internal canopy to the perimeter or lower edge of the main canopy. At high speed, the pressure on the small canopy tensions these lines and prevents the mouth of the main canopy from expanding. See, for example, U.S. Pat. No. 4,117,994. This technique, however, is very sensitive to tuning and manufacturing tolerances, and involves substantial labor in production.
Several other devices to control inflation characteristics of parachutes are shown in U.S. Pat. No. 5,209,436, U.S. Pat. No. 5,205,517, U.S. Pat. No. 4,955,564, U.S. Pat. No. 4,927,099, U.S. Pat. No. 4,588,149 and U.S. Pat. No. 4,065,079. However, the prior art has not previously provided a parachute inflation control device or reefing system which is simple, efficient, effective and reliable in controlling the inflation of conventional round parachutes, including the control of the shape of the lower edge, especially of large canopies.